Apparatus for making resilient bushings



May 10, 1938. o. B. wELKER APPARATUS FOR MAKING RESILIENT BUSHING 4sheet's-sheet 1 Original Filed April 25, 1936 @m /3 MENTOR I A/u,

s* ,mb ATTORNEYS.

May l0, 1938. o. awELKl-:R

APPARATUS FOR MAKING RESILIENT BUSHING 4 Sheets-Sheet 2 I )ly/EMDR.

Original Filed April 25, 1936 May 10, 1938.

B. WELKER APPARATUS FOR MAKING RESILIENT BUSHING 4 Sheets-Sheet 3Original Filed April 25, 1936 May 10, 1938. Vo. B. wELKER 2,117,046

APPARATUS FOR MAKING RESILIENT BUSHING Original Filed April 25, 1936 4Sheets-Sheet 4 INVENTOR.

BY @Maw `Patented May 10, 1938 UNlTED STATES PATENT oFElcE APPARATUS FORMAKING RESIHENT BUSHINGS AOscar B. Welker, Middletown, Conn.

This invention relates to apparatus for making resilient connections,which embody inner and outer` rigid members and an intermediate layer ofrubber or other elastic material. The present application is a divisionof my copending application, Serial No. 76,392 filed April 25, 1936,Patent Number 2,110,783, Mar. 8, 1938.

Many forms of elastic connections, or bushings of the type referred tohave been placed' upon the market, but experience has shown that thereare certain objections inherent in them. For example, in one form, thehollow rubber tube or sleeve has been assembled by first compressing itby inserting it into the outer tube andthen furmandrel before the innertube is inserted into place. The resulting connection is thereby limitedunder tension deectsrmore than when under compression, thereby allowingthe inner tube to move more readily out of center under dead load. Inmaking a connection lof this type, it is important that the rubber beplaced under a fairly high degree of stress, and that the stress bedistributed uniformly throughout the rubber, for this uniformdistribution results in greater frictional engagement with the inner andouter members and a longer life of the rubber. An effort to accomplishthis result has included a method of manufacture in which the rubbersleeve has been slipped onto an inner tube for a portion of its lengthand then compressed by reducing the diameter of the outer tube. Thismethod, however, did not permit alconnection to be made in unlimitedlengths. not distribute the stresses uniformly throughout the .length ofthe connection. y

Still another effort 'to obtain the desired degree oi compression hasbeen to mount the rubber sleeves in tandem between the inner and outertubes, and` then to draw them together axially by the use of bolts.

enumerated has included the curingV of a. mass of ther compressing it bythe use of an expanded` Moreover. it did rubber to the inner member andthen forcing the assembly endwise into an outer member. Under suchpractice, however, the rubbercan not flow on the bonded area and hencemost of the flow takes place on the unbonded area, and hence the`stresses are unequally distributed throughout the length of theconnection. A further'objection to the curing operation is the fact thatit is too expensive and that the length of bushing produced is limitedin length.

An object of my invention is to make an apparatus by means of which theintermediate layer of elastic material and a resilient connection is sostretched'at the time of its assembly that the stresses are uniformlydistributed' throu'ghout the length of the material.

Referring now to the'drawings, Fig. 1 is a top plan view of a machinefor making the resilient connections in accordance with my invention;Fig. 2 is a vertical section taken on the line 2 2 in Fig. 1 and shownon a scale larger than that of Fig. 1; Fig. 3 is anvend view of thetorsional bushing; Fig. 4 is a section taken on the line 4 4 in Fig. 3;Fig. 5 is a section showing a modified stretch curve of rubber th t isusually used in making torsional connections; Figs. 14 and 15 arelongitudinal sections showing the introduction of the stock and coreinto an outer member wherein the outer member is flared, and acts as adie for stretching, the stock; and Figs. 16 and 17 are secv tionssimilar to Fig. 5 illustrating modified forms.

.In Figs. 3 and 4, the resilient connection which is made in accordancewith my invention, comprises an inner member I0, an outer member Il 'andan intermediate member I2, all 'of which are shown as being cylindricalin shape and as having a common axis. The inner and outer members arepreferably made of metal, while the intermediate member is made ofelastic material, such as rubber. The present invention is concernedwith an apparatus for inserting the elastic sleeve in position betweenthe outer and inner members. It is understood that the inner member maybe either tubular or a solid shaft, and that the outer member may be anyobject whichhas an inside cavity ofa cylindrical shape, or even that ofa polygon.

The preferred manner of carrying out my invention comprises theformation of rubber stock into a long tube, the body of which isindicated at l5. One end of the tube is closed and the opposite end isopen. The closed end in one form of the invention may beformed by a plugi6, the outer end of which is reduced and is closely embraced by thestock. A ring embraces the stock at the reduced neck and cooperates withthe plug to impart strength to the stock at the closed end, so as toenable it to withstand the stresses that are incident to the stretchingoperation. The inner diameter of the stock is substantially equal to theouter diameter of the inner member l0, while the outer diameter of thestock is larger than the in ner diameter of the member I|. Consequentlyit is necessary to reduce the wall thicknessof the stock, and this Iaccomplish by stretching it during the assembly operation. v

The method by which I insert the elastic sleeve between the inner andouter members' comprises the insertion of a long continuous tube |00,into the stock until the forward end of it engages an annular shoulder20 at the innerend of the plug I6. The assembled unit is then placed ina machine and moved in an axial direction through a forming die 25,which partially reduces the diameter of the rubber sleeve from whence itis passed into thetube Ila, which further reduces it to the finishedsize. The tube lla. when removed from the machine becomes the outermember Il of the finished resilient connection.

Themachine, which I have shown forvstretching the rubber during theinserting operation, may comprise an open frame which has sides 30, andends 3| and 33 respectively. Between the ends there is a cross-member2|, which supports the die 25 and there are other cross members 22 and23, each of which supports one end of a tube Ha. In the illustrationshown, the end member 33 functions likewise as a support for one of thetubes Ila. While I have illustrated the machine as supporting threetubes Ila. in tandem relat1onship, it. is to be understood thatthemachine is capable of use with any number of tubes and that it may bedesigned for tubes of any length.

To force the stock into the outer member, I have shown an electri' motor35 which is adapted to rotate a gear 36 as by a belt drive 31. The gear36 has the bore thereof threaded for engagement with a threaded spindle38, which may be splined to a key 9 in one of the bearing caps 39. 'I'hespindle may have one end thereof connected to a carriage. 4| that ismounted for movement along the members 30. The connection is illustratedin detail in Fig. 10 wherein the end of the spindle has a ange 46 thatts loosely into an opening 26 in a plate 21 that is fastened to thecarriage. The carriage is provided with a saddle 42 in which therearward end of the tube Illa is adapted to be supported, the saddlebeing U-shaped s'o that the tube together with the assembled stockthereon may be quickly inserted within the machine. Itis to beunderstood that the axis of the threaded spindle is co-extensive withthat of the tube and with those of the tubes la. It is also understoodthat other means of forcing the rubber through the die may be employed,such as pneumatic or hydraulic rams lor pistons.

To use the apparatus, the tube Illa. is inserted into the rubber stockuntil it engages the closed end thereof whereupon the projecting end ofthe tubeis placed within the saddle 42. At such time 'ward end.of thestock into the die.

the neck of the stock is disposed between the carriage 4| and the die25. The motor is then started whereupon the operator guides the for- Hethen places one end of a tube lla into a U-shaped saddle 45 on the crossmember 22 and manually guides the other end to receive the moving' unitthat has passed through the die. The position of the parts at such timeis represented in Fig. 2. As soon as `the stock has entered such tube,the operator is then free to place another tube in the saddle 45a on thecross-member 23 and guide" it in the same manner to receive theforwardly moving stock. Ihe same operation is repeated until all of thetubes for which the machine has been designed have been assembled. It isunderstood lthat the length of the inner tube andof the rubber stock issuch that at the completion of the operation, the reduced neck projectsbeyond the farmost end of the last outer tube. Thereupon, the unitarystructurewhich comprises the tube loa, the stretched rubber stock andthe plurality of tubes ||a is lifted from the machine and the motor isreversed to return the carriage to its initial position. 'I'he assembledunit which is shown in Fig. 11 is then cutinto sections as along thelines af-a, each having a length of the outertube I la. so that thenished product corresponds to that shown in Fig. 4. If desired, however,the outer. tube may comprise an elongated member from which sections maybe cut transversely. In such case the tube supports 22 and 23 wouldbeeliminated and the tube would be supported on the end 33.

A modification of the rubber stock is shown in Fig. 5, wherein theforward end thereof is closed solely by the ruber wall which isreinforced by a thickened portion 60 to resist the stresses that areimparted to it during the stretching operation. To facilitate theuniform distribution of forces against the rubber, I insert a plug 6|which is rounded to conform to the shape of the inner end wall of thestock, and which has an annular shoulder 62 for receivinguthe tube Illa.I may also wish to force a rigid ring over the reduced end 60 toreinforce the rubber at this end in the stretching operation.

In-Figs. 16 and 17 there is illustrated new modied forms of rubberstock. At the forward end of such stock, I have shown a ferrule orsleeve 10 which is preferably vulcanized to the rubberformed,vas shownin Fig. 17.

In making the stock either in the form shown in Fig. 2 or in Fig. 5 therubber is cured onV a mandrel, which is removed before the tube |0a isinserted therein. In addition, the outer surfaces of the tube may besubjected to a grinding operation, so that its wall thickness may beuniform throughout its length. Moreover, to facilitate the entrance ofthe stock into the die and also into the outer tubes, I may applylubricant in the form of vaseline to the outer surface before the stockengages the die; I may also lubricate the outer .surface of theinnermember and the inner surface of the outer member previous to thestretching operation. This lubricant greatlyv reduces the frictionbetween the elastic material and the surface of the inner member and theinside surface oi the outer member during the stretching operation, andthereby greatly assists in the uniform distribution of stressesthroughout the length of the elastic material.

The reduction in size of the rubber stock through the die may comprisethe only reduction employed, although if desired, the stock may bereduced farther upon entering the outer tube. To facilitate thereduction, the opening of the die is tapered, as shown at 65 and thewall of the tube Ha is tapered, as atl 56. Due to the fact that theforward end of the advancing unit is unsupported, except by the die, therubber is free to flow, and hence the stretching stresses aredistributed uniformly. As a result, the finished vresilient connectioncontains confined rubber,

which is under a uniform state of stress to which it has been subjectedduring the forming operation, and hence the resilient connection iscapable of withstanding a maximum number of oscillations withoutevidence of fatigue.

In Fig. 12, I have shown a cross-sectional view through a modified formof a finished article, wherein 50 designates the inner rigid member,

| designates the outer rigid member, and 52the f intermediatelayer ofelastic material. In this illustration, the inner and outer members havea polygonal shape, and the inner member, in addition, is represented asbeing solid.- 'If desired, however, the inner member may be hollow asheretofore described in connection with the article which is illustratedin Fig. 4.

'Ihe chief` advantage of the article which is made in accordance withthe present method lies in the fact that the rubber or other elasticmater rial has been placedin tension throughout the length of thearticle, and that a predetermined percentage elongation of the stock ormaterial is maintained very uniformly from one end to the other.,' Theamount of stretch which may be' obtained is limited only by the ultimateelongation of the elastic material, although it has been found that forordinary torsional connections the amount of stretch need be only 100 to150% when rubber having a Shore durometer hardness of 60 to.65 is used.

,In Fig. 12, for example, there is shown a typical stress-stretch curveof the rubber that is usually used in torsional connections. The diagramin Fig. 12` shows the characteristics of the rubber.

when stresses up to 1000 lbs. per sq. in. are placed -upon it, thisbeing the range that would cover the use of most resilient connections.The ultimate strength of the rubber however, may be as high as 4000 lbs.per. sq. inch. The solid line curve designated 55 in Fig. 13 illustratesthe stress-stretch characteristic, whereas the broken line curvedesignated 56 shows the stress-hard ness characteristic of the rubber. e

An inspection of the diagram in Fig. 13 shows that whenever the rubberVis stretched an' appreciable amount. the hardness, and therefore theinternal pressure,A in the structure of the rubber increases. Forexample, according to the diagram, whenever the rubber is stretched only150% the relative hardness is increased from 60 to 75% or a relativeincrease of 21%.- The internal pressure in the structure of the rubber,as is evidenced by the increase in hardness, exerts a much greaterfrictional force against the walls of the outer and inner rigid membersof the resilient connection than would be possible i! the rubber werenot stretched. Moreover, thefact that the rubber is stretched uniformlythroughout the length o! the article insures a high frictional en# thatthe amount of stretch and likewise the stress which occurs in the rubberlin the ilnished resilient connection can be predetermined. Conversely,the outside diameter of the free rubber tube can be predeterminedwhenever a definite amount of stretch is desired in the nished bushing.For example, if one desires p percentage stretch in the rubber of thefinished bushing, then the rubber must be stretched an amount equal tothe product of (iooH) and original length of the stock, and the crosssectionalfarea ofthe free tube will be the prodand the cross-sectionalarea of the rubber in the finished bushing.

Assuming that: r equals ,the radius of the inside surface of therubber'in the finished bushing.

R equals the radius of the out side surface of the rubber in thefinished bushing.

R1 equals the outside radius l of the free rubber tube before thestretching operation.

'Ihen 1R2-1rr2=the area of cross-section `of rubber in the iinishedbushing.-

The initial cross-sectional area:

where (R1-r) represents the wall thickness of the free rubber tube, thatis to be stretched p percentage in order to completely ll the spacebetween the two metal members of the bushing.

Experience has shown that when vaseline has been applied to theouter'surface ofthe inner member and to the inner surface f the outerVmember, as well asto the rubber tube that is to be. stretched, therubber can be stretched very uniformly by this method. AThen after a fewhours have elapsed the rubber absorbs the vaseline and the frictionalresistance to twisting of one member with respect to the other is with-.stood entirely by the rubber. Experiments have further shown that thestress applied at the area of contact between thev rubber and the insidemember is practically equal to the stress in the body of the rubber; theaction probably conforming to the law of fluid friction. whereby thestress applied to the iluid is exerted equally in all directions.

Accordingly, I have provided a practical method of predetermining thefrictional engagement between the rubber and the inner and outer membersof the torsional bushing, and 'by this method sumcient stress can beplaced in the rubber by a predetermined calculation so as to withstand aspecied twisting moment which the rubber is expected to encounter; andby using rubber with a good resistance to permanent set, thestress inthe rubber can be maintained very near to that calculated over longperiods of time.

An important advantage, therefore, of articles which are made inaccordance with this Ymethod is that the stresses in the rubber and ofthe frictional engagement between the rubber and the retaining memberscan be accurately calculated in advance. A further advantage ofthemethod is the fact that the resilient connection may be made in anylength and then cut to the desired size, or if desired, a large numberof short bushings may be made at one time.` 'Ihe method, therefore,possesses economical manufacturing advantages, and assures uniformdistribution of .stresses in the stretched rubber. While the apparatusheretofore described included a die by means of which the stock isstretched as it is passed therethrough prior to its entrance into theouter tube, I may, in certain installations, utilize the outer /tubeitself as a die for effecting a stretched condition of the stock at thetime of its entrance into the tube.v In Fig. 14, for example, the outertube ll is ared, as at lll to provide a guideway for the stock, as it isforced into the tube. In this illustration, the ared portion likewiseprovides a shoulder, which abutsagainst the transverse beam 2i therebyholding the tube l firmly in position during the assembly operation.

In the modification of Fig. 15, the forming die is eliminated and oneend ofthe outer tube is ared as at 8 to admit the stock. The formationof the flared end 8 on the tube ll is permissible in those installationswhere adequate wall thickness in the outer tube may be provided, and insuch case, the tube is held against the transverse wall 22 in the samemanner as that illustrated in Fig. 1.

An important advantage of the method disclosed herein is the fact thatthe resilient connection may be made in any length and then cut to thedesired size, or if desired a large number of short bushings may be madeat one time. The method therefore possesses economical manufacturingadvantages as well as assuring uniform distribution of stresses in thestretched rubber.

I claim:

In a. machine for making resilient bushings having an outer tubularrigid member, a rigid innerJ member and an intermediate elastic member,comprising in combination Aa base, a plurality of supports on the base,means on the supports for holding a plurality of tubular outer members,between the supports in spaced relation and in axial alignment, saidsupports having openings aligning with the` openings in the tubularmembers, and means for forcing the inner and intermediate membersthrough a plurality of said tubular members, whereby the intermediateand inner members may be severed at the spaces between the tubularmembers without severing the tub lar members. OSCAR B. WELKER.

